Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)



Committee Chair(s)

Herman H. Weibe


Herman H. Weibe


George W. Welkie


Frank B. Salisbury


Thomas M. Farley


John O. Evans


The influence of the concentration of several solutes on the activity of succinic dehydrogenases from acetone powders of several species was studied spectrophotometrically. The plants used were: Cauliflower (Brassica oleraceavar. botrytis, L.), sugarbeet (Beta vulgaris, L.), sunflower (Helianthus annuus, L.), Halogeton glomeratus (M. Bieb) C. A. Mey., and Samphire (Salicornia rubra, A. Nels.). Sodium chloride, potassium chloride, mannitol, sucrose, glycerol, glucose, and Hoagland's solution, at increasing concentrations, were used.

Decreased (more negative) osmotic potential produced by sodium chloride, potassium chloride, and Hoagland 's solution resulted in a slight increase in' enzyme activity at low solute concentrations (π = -5 to -10 bars) but decreases in activity at higher solute concentrations (to about -130 bars).

Increasing concentrations of glucose and sucrose resulted in greatly increased succinic dehydrogenase activity.

Increasing concentrations of mannitol result.ed in increased succinic dehydrogenase activity, but the activity appeared to level off between an π of -9.3 and -15.8. Limited solubility prevented measurements at higher mannitol concentrations, so that it is impossible to say whether these would increase or decrease the reaction rate.

Increasing concentrations of glycerol in the reaction cuvette resulted in decreased enzyme activity.

Increased water stress, produced by repeat.ed wilting, did not cause changes in succinic dehydrogenase activity in sunflower plants.

It appears that osmotic potential is not the cause of variations in succinic dehydrogenase activity, since equal osmotic potentials produced by sodium chloride or sucrose led to almost opposite results. Instead, the species of solute and its concentration seem to be more important.

Halophytes (Halogeton and Salicornia) had about the same activity and reaction to various solutes as the other plants that were tested. It appears that at the osmotic potentials used, there were no significant differences in succinic dehydrogenase activity among the five species.



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